Method of tanning hides



Patented Jan. 22, 1935.

UNITED STATES PATENT OFFICE No Drawing. Application March '7, 1934, Serial No. 714,532

This invention relates to the art of tannin hides and particularly to a method or process wherein the length of time heretofore required in the tanning operation may be materially reduced. Reference is made to my copending application for U. S. Letters Patent filed November 17, 1932, Serial No. 643,053.

In the tanning of hides it is customary to soak the hides first thoroughly in clean water to first soak and open up the fibers as much as possible and secondly to loosen the scurf, putrefactive refuse, dirt and epidermis. Following this initial soaking, the hides are then placed in a solution of lime and water and/or other saponifying and depilatating materials, following which treatment for the proper length of time, the hides are then fleshed and unhaired. The hides then have the interfibrillar substance rendered soluble and the fibers somewhat distended.

Heretofore in producing sole leather, only a small portion of the lime or other alkaline materials used in the above indicated step were neutralized and removed before the hides entered the actual tanning liquor, but I find advantages, in producing heavy leather, in completely neutralizing these alkaline materials and allowing the salts and products therefrom to remain'in the hides for the purpose of giving solidity and increased weight thereto by use of some neutralizing agent as the first step in the rockers prior to subjecting the hides to tanning liquors. However my invention herein described applies equally well to either practice.

In practicing my. invention in'the form as now best known to me, the hides after being prepared in either case as above indicated, are

then placed in a very weak and somewhat aged solution of water and tanning materials and are allowed to remain in this solution or mixture until the tanning material bites or colors the outer surface of the hides. This coloring of course, actuallymeans that the very thin outer portions or surfaces of the hides have actually been converted into leather. In the case of vegetable tanning hides to produce sole leather, this coloring process should require not to exceed two hours and the strengthof the tanning liquor recommended is somewhere around 10 barkometer. The color desired is a delicate bite.

The hides, following this coloring step will then contain water probably around 75% of the total weight, the remaining 25% being hide fibers more or less. Each hide is. of course,

made up of innumerablefibers which become more or less distended by the water content, the water itself filling in the spaces therebetween.

The succeeding step following the coloring step consists of immersing the hides in an oil having certain properties which will hereinafter be pointed out more specifically. I have found that heavy cow hides may remain in this oil for several days and that the oil replaces the water and plumps the hide to a much greater extent than did the water. the hide is relatively greater for periods of time recommended as the minimum. -This minimum for sole leather hides is 24 hours which should produce leather of 8 to 9 iron on the backbone.

Following the period of immersion in the oil, the hides are removed and immersed directly in a relatively strong solution of tanning materials and in the case of vegetable tannage I have found that a strength in barkometer of from to 90 works satisfactorily and that the speed of tanning seems to increase as the strength of the tanning material solution is increased. However, lower and greater concentrations of tanning liquors will operate successfully, the determining factor being the character of the hides and leathers and speed of tanning desired.

.should be older and controlled to have a slightly acid reaction so as to further neutralize the alkalines carried by the hides. I further recommend'that the tanning liquor employed have its tannin content maintained during the tanning process. I have found that it is possible The plumpness of to have the hides completely struck through in pense of mixing extracts, a reduction in the expense of operating pumps, and most important -the shortening of the period of time for tanning the hides, which reduced period means a reduction in the investment in hides as well as giving the tanner the advantage of keeping closer to the raw stock market with a more rapid turnover of his capital, thereby eliminating the tremendous loss that has frequently occurred in this business of tanning because of the speculative character of the raw stock market.

The new process constituting my invention has been more or less generally described above. Asan example of how the process is commercially carried out, a commercial procedure will 'now be described. Fourteen vats are arranged in two rows of seven vats each, the vats being hooked up into a press system whereby each vat may receive at its bottom the liquor from the top of the preceding vat. This flow is arranged and secured by means of a pipe having an opening near the surface of the preceding vat and having a discharge into the succeeding vat near its bottom so that raising the level of the liquor in the preceding vat will set up the flow. Now assuming that this system of vats is filled and one lot of hides has been taken from vat No. 1 which was the oldest pack, and that the liquor from this vat has been removed to a storage tank for strengthening and cleansing, a new pack of hides is placed in this No. 1 vat to have the hides or. sides hung on the customary rocker frame. It is to be understood that the hides now referred to as being placed in vat No. 1 have been initially placed in the water and lime solutions, and have been fleshed and unhaired and/or have had such treatment or washing as desired. The weak coloring solution above'described is pumped into this vat No. 1.

Vat No. 14 is adjacent to vat No. 1 and contains the oil above referred to and also the pack which was placed therein the day before. Vat No. 2 then contains the oldest pack, the hides of which will come out tomorrow. Now going back to vat No. 1, the hides which have just been placed therein are colored in the course of about two hours, following which period of time, this coloring solution is pumped back into a storage tank then leaving vat No. 1 in a drained condition. The heavy liquor which was pumped out of vat No. 1 before placing the hides therein is then pumped into vat No. 2. Vat No. 2 already being filled with liquor then starts overflowing into vat No. 3 by reason of the heavy liquor being added thereto. However since all of the vats are hooked together as above indicated, the overflowing of one vat into the other will cause a like fiow between all the vats on around to vat No. 14. Since vat No. 14- is the one in which the oil is contained, the overfiow from vat 13 entering under the oil in vat 14 will cause the oil to rise in vat 14 and thus overflow into vat 1. When this overflow of oil into vat 1 has been accomplished, all of the heavy liquor originally taken from vat No. 1 and pumped into vat No. 2 has been discharged into vat No. 2. Now 24 hours later the same steps are repeated, the then oldest hides being removed from vat No. 2,.the coloring liquor placed in vat No. 2 for two hours and removed, the strong tanning solution from vat No. 2 pumped from the storage tank into vat No. 3 to carry the oil from vat No. 1 into vat No. 2.

Thus it is to be seen that the oil is gradually worked around from one vat to the next in the proper sequence following the coloring of the hidesand that the strong tanning solution falls impurities or foreign matter.

into the vat upon the removal therefrom of the oil. I have found that this oil can be used over and over again indefinitely and that the only. addition of oil necessary is that to replace loss from leakage and that which will attach itself to the vats so that this oil material can be considered to be practically a permanent quantity. There is no drumming required with this process during the period of tanning but I have found that in handling hides, there is a tendency, particularly with hides having very light bellies, for the bellies to try to float upwards when the tanning liquor is run into the vat immediately after the oil has been removed and in such cases I have found that by hanging the hides or sides with the bellies up and the backs down, this tendency is overcome.

The foregoing steps have been described without reference to the step of neutralizing the lime in the hides. When complete neutralization is desired to leave the salts in the hides, I introduce another vat into the system, into which vat the previously limed hides go. A neutralizing solution is put into this extra vat, the hides immersed therein to effect the lime neutralization, the neutralizing solution removed, after which, the steps are followed as above outlined without removing the hides from the vat-a fifteen vat system then being employed in place of the fourteen vat system.

The process above described and constituting my invention comprises essentially the initial preparing of the raw hides by liming and otherwise, the step of initially coloring the hides, the step of replacing the water content of the hides with an oil, and the succeeding step of replacing the oil with a tanning solution of strong concentration. My invention further comprises the control of the interchange of the oil with the water and the tanning solution with the oil. The control is effected by use of certain oils, and before describing the essential properties of such oils, it would perhaps be better to explain what I believe to be the theory of operation.

Initially water enters the hides to distend the fibers and fill the spaces therearound through capillary action. Capillary action is produced by the motive force 'of differences in surface tensions of the water and the hide fibers. In other words employing the molecular theory, the water, in order to penetrate the hide must have a greater adhesion with the hide fibers than its cohesion.- In employing the terms adhesion and cohesion, they have their true meanings in that the force of cohesion is considered as being exerted between like molecules while the force of adhesion is exerted between unlike molecules, both forces being due to molecular attraction. It is further to be considered that the surface tension of a liquid varies with concentration of the solution and that the surface tension of water is rapidly reduced by the adding thereto 01' Another fundamental proposition to be considered is that where two liquids are in the presence of a solid, a motive force will be set up such that the liquid having the smaller surface tension will replace along-that solid the liquid having the. greater surface tension. The rate of this interchange will vary due to a number of factors, one such being the rate of absorption which would tend to delay the movement.

Now when the water-filled hide is immersed in the oil, the oil having a surface tension lower than that of the hide contained water will at once start displacing the water due toits lower surface tension so that within a short period of time (24 hours as above indicated) the oil will have struck'entirely through the hide and will have so'filled the spaces bet-ween fibers as to have plumped it up to increase its actual thickness as comparedvto that when filled with water. The hide thus filled with oil is then immersed in the tanning solution and a reverse procedure is obtained. The surface tension of the tanningsolution is less than that of the oil so that the tanning solution then enters the hide and the oil is carried out' and floats to the surface of the bath of tanning solution. In other words the first step, the surface tension betweentthe' oil and hide fibers is less than that-between the water and hide fibers while in the second step, the surface tension between the-tanning solution and the hide fibers is less than that between the oil and hide fibers.

It is observed that during the step of replacing the oil with the tanning solution, the replacement occurs more'quickly atthe lowermost parts of the submerged hides than it' does at the upper portions. This would be expected in,

that the density of the tanningsolution varies from near the surface to the bottom of the vat, increasing with depth and that the densersolution would have less surface tension with respect tothe hide fibers than would the less dense solution.

The oil employed may have a wide range of densities. In fact the process above indicated may be successfully performed byusing an oil having a specific gravity as low as .73 which would be in reality a good grade of gasoline. The use of gasoline as-the oil above referred to is very effective and gives a good color to the leather. There is the possible objection, however, to the use of gasoline in that it might leave an odor in the leather even after tanning and that it might carry out some of the natural oils or fats preferably to be retained by the hides. In-

sofar as the process is concerned, however, this light oil operates very successfully. Oils ranging on up to a specific gravity of 1.17 have also been used very successfully. These heavier oils have been derivatives of coal; tar and creosote oils. Mineral oils of the petroleum series are indicated as being preferable since they are readily obtained at a comparatively low price in quantity and may be had without odor. Common fuel oils (odorless) are giving very good results. Lard oil will replace the water in the hides and'seemingly plump the hides beyond that condition achieved by other oils. However, its cohesion and its adhesion to the hide fibers are such that it is not easily replaced by the tanning solution, at least in thesame length of time in which the other oils are replaced, and

in fact there seems to be no interchange between,

the tanning solution and the lard oil. Codfish" oil does not seem to penetrate the hide initially effected by sediment or impurities. A neutral that of water and greater than that of the tanning solution to be used, it being kept in mind that the tanning solution employed is one which has a greater strength than that which would be permissible in the customary tanning operations following at once the initial coloring step. a

The advantage of employing the oil, which employment is entirely foreign to previous concepts in the tanning of hides, is that the strong tanningsolution may be employed and yet controlled in effect so, that the actual tanning operation is speeded up as above. indicated.

The coloring of the hides to produce an initial surface leather is accomplished with the weak tanning solution in a slightly acid condition.

Not only is the alkaline material in the surface of the hide th'en neutralized, but that material is removed from the water at the surface, thereby giving, it is believed, .a water solution at the surface with a slightly greater surface tension than that of the solution within the hide. Thus, by coloring thehides first before immersion in the oil, I secure a hide surface which is in a better condition to initiate the interchange of the oil with the hide contained water than were the uncolored hide directly immersed in the oil. That'is, the adhesion of the oil with the tanned fibers at the surface is believed to be slightly greater than that with the raw fibers, and thereafter, the adhesion of the tanning liquor with those surface tanned fibers slightly exceeds that with the oil covered raw fibers. In any event, such coloring is found to speed up the final tanning without damage to the hides.

I claim:

1. The method of tanning hides which consists of soaking the hides in water and liming them; fleshing and unhairing the hides, coloring the hides with a tanning liquor to produce a leather surface, covering the colored hides with an oil which will plump the hides and replace water therein, and-then immersing the oil plumped hides in a relatively strong tanning liquor, said oil being of that further quality which causes the oil to be displaced by the strong liquor.

2. The method of tanning hides which con--' sists of soaking hides in water and liming, coloring the hides to produce a surface leather, immersing the colored hides in an oil having less surface tension than that of water whereby the oil will cause dehydration of the raw interior of the hides, and then immersing'the hides in a tanning liquor having a surface tension .less than that of the oil.

3. The method of tanning hides which consists of soaking the hides in water and lime solution giving the hides an appreciable water content, immersing the water soaked hides in an oil having less surface tension than water and allowing the oil to strike completely through the hides, and then immersing the oil bearing hides in a tanning solution having less surface tension than the oil.

4. The method of tanning hides which consists of dehydrating and plumping water soaked hides by an oil, and then immersing-the oil plumped hides in a tanning liquor to permit automatic replacement of the oil by the liquor.

5. The method of tanning hides'which consists of coloring water soaked hides, dehydrating and plumping the hides with an oil, and then immersing the oil bearing hides in a tanning liquor.

8. The method of tanning hides which consists of initially subjecting the hides to an alkaline solution, coloring the hides with a weaktanning liquor to effect a surface bite only, covering the colored hides with an oil which will pro duce dehydration of the hides and strike therethrough, and then immersing the oil bearing hides in a tanning liquor.

7. The method of tanning hides which consists of initially subjecting the hides to an alkaline solution, coloring the hides with a weak tanning liquor to effect a surface bite only, covering the colored hides with an oil which will produce dehydration of the hides and strike therethrough, and then immersing the oil bearing hides in a tanning liquor, said weak tanning liquor being in a slightly acid condition.

" a. The, method of tanning a. hide by utilizing atanning liquorof 60 degrees barkometer or more which consists of first soaking the hide during which soaking the hide takes up considerable water,-then limingv the hide, coloring the hide with a tanning liquor around 10 degrees barkometer, automatically replacing water in the hide by placing in contact therewith an oil fibers than the water but having less cohesion,

allowing the hide to remain subjected to said oil sufficiently long to permit the oil to strike through and plump the hide and replace water, and immersing the oil bearing hide in a strong tanning liquor having more adhesion with the hide fibers than the oil but less cohesion.

. solution.

10. The method of tanning a hide which consists of liming the hide, completely neutralizing the lime within the hide, coloring the hide, dehydrating the hide by covering it with an oil, and replacing the oil with a tanning solution.

11. The method of tanning a hide which consists of liming the hide, completely neutralizing the lime within the hide, dehydrating the hide by covering it with an oil, and replacing the oil with a tanning solution.

12. A method of tanning hides which consists of first performing the usual beam-house steps, placing the hides in a vat, running a weak tanning solution into the vat to color the hide, replacing the solution by an oil, and replacing the oil with a tanning material.

l3. The-method of tanning hides by a press system of vats, wherein the hides are left in the vats until struck through, which consists of placing a weak tanning solutionin one of the vats forjhidecolo'ring, placing an oil" in an successively advancing the oil from oneQvat to the other by flowing tanning liquor therunder. 15. In a method of tanning hidesiby' al press system of vats wherein the hides are left'jin the vats until struck through, those steps oi 'fllling one of the vats with an oil having less surface tension than the tanning liquor emplo'yedQand successively advancing the oil from one vat to the other by flowing tanning liquor thereunder, and flowing in and out of the vat' immediately ahead of the oil a weak tanning coloring HAROLD M. GUSDORF. 

